Telephone-switchboard system.



No. 686,272. Patented Nov. 12, MN.

I r. w. DUNBAB,

TELEPHONE SWITCHBUARD SYSTEM.

(Application filed Aug. 17, 1900.) (No Model.) 3 Sheets-Sheet I.

x Wig rm: NORRIS PETERS co. Pnorouma, WASHINGTON. u, c.

No. 686,272. Patented Nov. l2, I90l.

F..W. DUNBAR.

TELEPHDNE SWITCHBOABD SYSTEM,

(Application flled Aug. 17, 1900.) (No Model.) 3 Sheets-Sheet 2.

m: NORM: PETERS 00. F'HDTC-\ITNO,WA5HINGTON. o. c.

No, 686,272. Patented Nov. 12, 190i.

F. W. DUNBAR.

TELEPHONE SWITGHBOARD SYSTEM.

(Application filed Aug. 17, 1900.)

(No Model.) 3 Sheets-Sheet 3.'

13 & 161 .6

QZifir 0 UNITED STATES LATENT OFFICE;

FRANCIS IV. DUNE-AR, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGGSVVITCHBOARD' AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

TELEPHONE-SWI'TOHBOARD SYSTEM.

SPECIFICATION forming part of Letters Patent No. 686,272, dated November12, 1901. Application filed August 17, 1900. Serial No. 273131. (Nomodel.)

To aZZ whom i mat concern.-

Be it known that I,FRANoIs W. DUNBAR,a citizen of the United States;residing at Chicago, in the county of Cook and State of Illi-' nois,have invented a certain newand useful Im provementinTelephone-Switchboard Systems, (Case No. 7,) of which the following is afull, clear, concise, and exact description, reference being had to theaccompanying drawings, forming a part of this specification.

My invention relates to a telephone-switchboard system, my object beingto provide an improved system of circuits and improved form of telephoneapparatus at the central station. I

In telephone-switchboards as usually constructed heretofore thetelephone-line is normally connected with one or more springjacks orconnecting terminals at the central station, the telephone-line usuallybeing connected with a single connecting terminal in the case ofa-single or divided board and with a plurality of connecting terminals,one upon each of the several sections, in the case of a multipleswitchboard. These spring-jacks or connection terminals are individualto the respective telephone-linesthat is, each line is connected with aconnection terminal or terminals which belong to that line alone. Inthese exchanges of the prior art the springjacks or connecting terminalshave been permanently connected with the telephone-line. The individualannunciator or call device by means of which the subscriber attracts theattention of the operator at the central station has been connectedeither permanently with the telephone-line or has been arranged so thatthe act of making a connection with the telephone-line at the centralstation serves to disconnect the individual annunciator. Since theindividual annunciator and the spring-jack or connecting terminal areboth normallyconnected with the line \vhenthe same is not in use forconversation, it frequently happens that the insertion of aconnectingplug serves to accidentally actuate the annunciator at thetime when the same should remain inert, and this fact leads todifficulty in many telephone systems, and, moreover, the fact that theindividual annunciator and the connecting terminal are both normallyconnect-ed with the line at the time when the same is not connected forconversation limits the number of different circuit arrangements whichmay be employed. In accordance with the present invention thespring-jack or connecting terminal individual to each line is normallydisconnected from the telephone-line and is adapted to be connectedtherewith when connection is made with the line. I preferably providemeans whereby the act of inserting the plug in the spring-jack orconnecting terminal serves to automatically connect the spring-jack orconnecting terminal with the telephone line. The act of removing theplug at the end of the conversation serves to automatically disconnectthe spring-jack or connecting terminal from the telephone-line. Inpractice I employ a relay adapted when energized to actuate the switchwhich serves to connect the spring jack with the telephone-line, thecircuit through the relay-magnet being closed by the act of insertingthe connecting-plug in the springjack, the removal of the plug from thespringjack serving to deenergize the relay-magnet to disconnect thespring-jack from the telephone-circuit. In the case of multipleswitchboards the plurality of spring-jacks may be controlled by a singlerelay, whereby the same may be connected with the telephonecircuit whenconnected for conversation and disconnected therefrom at the terminationof the conversation. I also associate the individual or callingannunciator with the apparatuswhich controls the circuit through thespring-jack, whereby the act of making connection with the line servesto disconnect the individual annunciator. I preferably arrange thecircuit so that the individual annunciator is disconnected from the lineat ap-' proximately the same time that the springjack is connectedtherewith and so that'the disconnection of the spring-jack from thetelephone-line is accompanied by the practically simultaneous connectionof the individual annunciator therewith. The individual annunciator thusbeing disconnected from the spring-jack when the plug is insertedtherein, the danger of, inadvertently the test-ring.

to be made.

actuating the individual annunciator is -entirely removed. Moreover,since the springjack is entirely disconnected from the telephone-circuitwhen the connecting-plug is inserted in the spring-jack the danger ofinadvertently actuating any apparatus connected with the telephone-lineis removed. This feature of my invention is equally applicable andadvantageous in systems of the centralenergy type and systems of thatclass in which the energy for the talking-currents is supplied from thesubstations. For multiple switchboards I preferably arrange the relaywhich controls the circuit through the springjacks so that the same willcontrol the test ing-circuit. For the purpose of the busy test I usuallyemploy a source of electricity adapted to be connected with test-ringson the'several spring-jacks or switch-sockets. If the busy condition ofa line is to be denoted by a click, the source of electricity isconnected with the several test-rings when connection is made with theline, while if a silent test is desired the source of electricity isdisconnected from the test-rings when connection is made with the line.In the former case the operator hears a click in her telephone if theline is busy when she touches the plug to In the latter case thetelephone remains silent when the line is busy. By employing the relaywhich controls the circuit through the connection terminal for alsocontrolling the testing-circuit the act of making connection with theline serves to operate the relay, which thereupon connects the terminalwith the line and at the same time connects the testing-circuit incondition 5 to give the proper test-signal.

I have illustrated my invention in the accompanying drawings, in which-Figure 1 is a diagram illustrating my invention as applied to atelephone-line having a diagram illustrating two telephone-linesconnected with a multiple switchboard at the central station, thetelephone-line being provided with selective signaling apparatus wherebythe subscriber may in a well-known manner select the division of theswitchboard 'at the central station at which connection is Fig. 4: is aside view of the relay which I preferably employ. Fig. 5 is a sectionalview thereof. Fig. 6 is an end view thereof. Fig. 7 is a plan viewthereof.

Like letters refer to like parts in theseveral figures.

As shown in Fig. 1, the line of subscriber A extends in two limbs o a tothe central station, where the same are connected, respectively, withthe springs a a carrying armatures and adapted to be actuated by therelaycoil 1). The spring a normally rests against back contact 01;, andthe spring a normally rests against back contact of. Between thecontacts 01; and a the coil of the individual annunciator o isconnected. The spring a? is adapted when the relay-magnet is actuated toengage the front contact a, which is connected with the terminal at ofspring-jack d. The spring a is likewise adapted to engage the frontcontact a which is connected with the line-terminal (1 Moving with theterminal d, but insulated therefrom, is a contactterminal 61 adaptedwhen the connectingplug e is inserted in the spring-jack to engage thecontact-plate al which is connected with the ground. The contact (1 isconnected through the winding of relay 1) and through the battery b toground.

It will be noted that the spring-jack d is normally disconnected fromthe telephoneline a, a, while the individual annunciator c is normallyconnected therewith. When the subscriber desires to be connected forconversation, he sends current in the usual manner over the limbs a aand through the individual annunciator 0, thereby actuating the same andcalling the attention of the operator at the central station, whothereupon inserts the answering-plug e in the spring-jack d. The tip 6of the plug 8 engages spring cl, and the sleeve 6 thereof engages theterminal 01 The spring d is thus moved laterally, thereby carryingcontact d into contact with contact d and the circuit of battery I) isthus closed from ground through relay-magnet 1), contacts 01 CF, toground. The relay is thus energized, thereby attracting the armaturescarried upon springs a a and moving the same out of contact with theirrespective back contacts a a and into contact with their respectivefront contacts a M. The individual annunciator c is thus disconnectedfrom 'the telephone-line a a, and the spring-jack d 'is connected withthe said telephone-line. Then the conversation is completed and theoperator removes the plug 6, the circuit through battery I) is openedand the relay magnet is deenergized, thereby permitting the springs a ato return to the back contacts to thereby connect the individualannunciator with the telephone-line and to disconnect the spring-jackfrom said telephoneline.

In Fig. 2 I have illustrated two telephonelines extending from thesubstations to the central office and adapted to be associated with theseveral spring-jacks of a multiple switchboard, three sections of theswitchboard being shown for the purpose of illustration and description.Each of the subscribers is provided with a microphonefand a receiverf,themicrophone being included with a batteryf in a local circuitwith theprimaryf of an induction-coil, the secondary f of which is connected incircuit with the receiverf and the limb a of the line. The limb a of theline is connected with the switchhook f which normally rests againstcontact f and which when the receiver is removed is adapted to engagecontacts f and f The bell f is included in circuit between the contact fand the limb ct. The calling-generatorf is included in the usual mannerin circuit with the bellf". The limb Ct terminates, as in Fig. 1, at thespring a while the limb a terminates at the spring a The spring avibrates between the contacts a and a, while the spring a vibratesbetween the contacts a and of. The individual annunciator c is connectedin circuit between the contacts a and agwhile the contacts a isconnected with the springs d d of the plurality of springjacks d d. Ihave illustrated three sections, 0, D, and E, and one of thespring-jacks d of each of the telephone-lines A and B is mounted at eachsection of the switchboard. The contact a is connected with theterminals 01 of the several spring-jacks, and associated with the spring01' at each spring-jack and insulated therefrom is the contact (iadapted to make contact, when the plug is inserted, with the contactMounted to move with the spring a and insulated therefrom is a spring aadapted, when the relay is energized, to engage contact a", which isconnected with a test-ring d at each spring-jack. A battery g has onepole connected to ground and the other pole connected to spring a Thewinding of relay b is connected on one side to the ground throughbattery I) and on the other side to the springs 61 of the severalspring-jacks. Instead of employing the two batteries 1) and g a singlebattery may be employed. I have lettered the circuits and apparatus ofthe telephone-lines A and B with the same referenceletters, since thetelephone-lines, as illustrated, are in every respect alike.

The tip 6 of the answering-plug e is connected to the tip-strand tof thecord, and the sleeve 6 of the plug is connected with the sleeve-strands.

' connected with the tip 71/ of the calling-plug h, and thesleeve-strand s is connected with the-sleeve h of the connecting-plug. Akey 7c is adapted when depressed to connect the operators telephone setbetween the strands, and the key l when depressed is adapted todisconnect the answering-plug from the calling-plug and to connect thecallinggenerator in circuit with the calling-plug. The callinggeneratorm is connected between the back contacts 1 Z of the ringing-key Z. Theoperators telephone-receiver 0 and the secondary 0 of the induction-coilare connected between the back contacts 71: k of the listening-key k andthe primary 0'. The microphone 0 and the battery 0 are included in alocal circuit. A ground-leg 0 including an impedance-coil 0 is connectedbetween the receiver 0 and the secondary 0. The clearing-outannunciatorp is connected between the tip and sleevestrands t and s.

The operation of the system is as follows: Supposing that subscriber Adesires to converse with subscriber B, he removes his telephone-receiverfrom its hook and operates his The tip-strand t is likewise generator,thereby sending current over limb a, spring a contact a individualannunciator 0, contact a, spring a back to the gen erator over limb a.The individual annunciator c is thus actuated to notifythe operator atthe central station. The operator thereupon inserts the answering-phi ge in the spring-jack at the section of the switchboard at which she islocated, thereby moving spring (Z into contact with the contact (1 Thecircuit of battery b is thus closed through winding of relay 1), springd contact 61 to ground, and back to battery I). The relay 1) is thusactuated, thereby moving the springs a and a out of contact with theback contacts a and a respectively, and moving said springs intocontact, respectively, with contacts a and Q The individual annunciatoris thus removed from circuit and the spring-jack is connected with thetelephone-line a a. The spring a is at the same time moved into contactwith contact 0,, thus connecting battery 9 with the test-rings d d ofthe several spring-jacks. The operator then depresses key it to bridgeher telephone set in circuit and receives from subscriber A the numberof the called subscriber. Learning that connection is desired withsubscriber B the operator lifts the connecting-plug h, which is thecompanion to the answering-plug e, and touches the tip thereof againstthe test-ring d of the spring-jack belonging to subscriber B andsituated at section 0 of the switchboard at which the operator islocated. If the line of subscriber B is connected with anothersubscriber, the battery g of subscriber B will be connected with thetest-rings 01 and when the tip of plug h is touched to this test-ringcircuit will be closed from battery g through springs a contact a",test-ring d tip 7L, contact of the listening-key, through receiver 0 andgroundleg 0 back to battery g. The operator will thus hear a click inher telephonewhen the tip of the plug is touched to the test-ring, andwill thus know that the line is busy. If the operator hears no click,she will know that the line is not busy and will insert the plug h inthe spring-jack of subscriber B, thereby actuating the relay 1) ofsubscriber B to connect the spring-jack with the line of subscriber Band to disconnect the individual annunciator. The operator thendepresses the ringing-key Z and sends current through the bell ofsubscriber B. When subscriber B removes his telephone from the hook, thesubscribers are connected for conversation. The talking-circuit may betraced from limb a of subscriber A through spring a contact a, spring61, tip 6, strand t, tip h of plug 71., spring d of spring-jackbelonging to subscriber B, contact a", spring c limb a of subscriber Bthrough his talking apparatus, thence by limb a through spring a.contact a terminal (Z plug-sleeve 7L2, strand .9, plugsleeve e terminal(1 contact a spring a to limb a, and thence throughthetalking apparatusof subscriber A. When the subscribers have finished theirconversation,they hang up their receivers and one or both of thesubscribers actuate the generators at the substations, thereby sendingcurrent through the clearing out annunciator p in a wellknown manner toconvey the signal of disconnection to the operator at the centralstation. Thereupon the operator removes the plugs e and h, and thecircuit of batteries 1) I) being opened the relays b b are denergized,thereby disconnecting the spring-jacks and connecting the individualannunciators c c in circuit to respond to another call for connection.

In Fig. 3 I have illustrated my invention as applied to a telephonesystem of that class known as the divided multiple, in which means areprovided whereby the subscriber may select the division of the multipleswitchboards at which connection will be made. With the exception of theindividual annunciators and the test-circuit at the central station andthe calling apparatus at the substation the apparatus shown in thisfigure is the same as that illustrated in Fig. 2, and like parts havebeen indicated by the same reference-letters as those employed in Fig.2. Each subscriberis provided with a plurality of individualannunciators at the central station, in the present instance four, 0 c 00 one being located at each division 0 D E F of the boards. The coils ofannunciators c and c are connected in series and are placed between theback contactsa and a of relay 1). The annunciators o and c are connectedin series in a grounded leg from that side of annunciator c which isconnected with back contact a. At the substation a generator to isprovided which is adapted to send current of positive or negativepolarity, as desired. Generators of this class are well known, and Ihave illustrated the same diagrammatically. One side of thearmature-winding of the generator is connected with the limb a of theline, and two brushes w 10 are provided for the generator, one connectedwith keys '0 and 12 while the other is connected with keys 1; and c.When the key 2; is depressed, the generator to is connected between thetwo limbs a a of the telephone-line, so as to send current of negativepolarity thereover to thereby actuate annunciator c, which is polarizedto respond to current traversing the coil in a negative direction only.\Vhen key 0 is depressed, the generator to is connected between limb aand ground, thereby actuating annunciator c, which also responds tocurrent of negative polarity. Likewise the depression of key n willconnect the generator between the two limbs of the line to send currentof positive polarity, thereby actuating annunciator 0 While thedepression of key 0 will connect the generator between limb a and groundto send current of positive polarity thereover to actuate annunciator 0The several annunciators are mounted upon the respective divisions O, D,E, and F of the switchboard, and the subscriber is thus enabled toselect the division at which the connection is to be made. In thisfigure the testing system instead of giving a click in the operatorsreceiver when the telephone is busy will remain quiet when thetelephoneline is busy and will give a click when the line is idle. Itwill be noted that the spring a instead of normally resting out ofengagement with the contact a", as shown in Fig. 2, normally rests inengagement therewith, so that the battery 9 is normally connected withthe test-rings and is adapted to be discon nected therefrom when therelay-magnet b is energized. When the operator therefor touches the tipof the plug to the test-ring, she will hear a click if the line is idle,while if it is busy she will fail to hear the click. It is obvious thateither system of testing-that is, silence or a click to indicate a busylinemay be used, according to whether the contact a is on the back orfront side of the spring a This system illustrates the manner in whichcircuits may be employed in accordance with the present inventionwhichcould not be employed were the spring-jack or connectingterminalpermanently connected with the telephone-line, as has been the usualpractice heretofore. Thus it will be noticed that when the plug 6 isinserted in the spring-jack the sleeve 6 of the plug serves tomomentarily connect together the test-rings d and the sleeve or terminal61 of the spring-jack. In the absence of the relay 1) and the contactscontrolled thereby the circuit of battery g would flow to the test-ringd thence through the sleeve of the plug to the terminal d of thespring-jack, thence over the line connected therewith through contacts aand of, which would in that case form a continuous conductor, and thencethrough the grounded annunciators c c. back to the battery. One of theseannunciators would thus be actuated, depending upon the direction of thebatterycurrent, and a signal would be inadvertently conveyed to theoperator at another board by the act of making the connection with theline. By the employment of the present invention, wherein thespring-jack is normally disconnected from the individual annunciator athrough the agency of the contacts at the relay, this inadvertentactuation of the annunciator is avoided.

While I have illustrated my invention in connection with substation andcentral-station apparatus of specific character, it will be understoodthat I have done so merely for the purpose of fully describing myinvention and that the essential features of my invention are equallyapplicable to substation and central-station apparatus of otherconstruction and design.

The relay, as shown in detail in Figs. 4 to 7, inclusive, is providedwith a core 6 upon which is mounted the winding h The core is mountedupon the shell I), which completes the magnetic circuit, and thearmature b is pivoted at b and carries in the free end a block ofinsulation b adapted to engage and actuate the contacts when thearmature is attracted. Upon the shell b and insulated therefrom are twocontact-plates a a, carrying on the upper faces contact-points normallyengaged by contact-points upon the springs a a respectively. The ends ofthe springs a a are adapted to be engaged by the end of the block b onthe armature, and when the armature is attracted to move this blockinward the spring a is moved into contact with the spring-plate a andspring 0. into contact with spring-plate a The central spring a isadapted when the armature is attracted to be moved into contact withspring-plate a". The end of the spring a -is bent down over the end ofblock Z) to limit the outward movement of the armature. The severalcontacts and springs are connected in circuit, as shown in Figs. 2 and3.

While relay-springs have been referred to herein and are preferred, itwill be understood that levers or any movable part actuated by a magnetmay be employed.

Throughout this specification I have referred to spring-jacks,connection-terminals, and switclrsockets. Where these terms are used inthe following claims, I desire it to be understood that they refer tosuch organizations as a whole rather than to their individual parts; butWherever in the said claims a portion only of the spring-jack is meantsuch distinction is clearly pointed out.

Having described my invention, what I claim as new, and desire to secureby Letters Patent, is-

1. The combination with acallingtelephoneline, of an individualconnection-terminal for the line normally disconnected therefrom andmeans for automatically connecting said terminal with the line when aconnection is established therewith in response to the call,

therefrom when not in use, substantially as' described.

at. The combination with a calling telephoneline and an individualconnection-terminal for the line normally disconnected therefrom, ofmeans actuated by the act ofmaking connection with the line in responseto the call for connecting said terminal with the line, substantially asdescribed.

5. The combination with a telephone-line and an individualconnection-terminal for the line normally disconnected therefrom, ofmeans actuated by the act of making connection with the line forconnecting said terminal with the line, and means actuated by the act ofunmaking connection with the line for disconnecting saidconnection-terminal from the line, substantially as described.

6. The combination with a telephone-line and an individualconnection-terminal for the line normally disconnected therefrom, ofaline-signal, a relay distinct from said signal for connecting saidterminal with the line, and means actuated by the act of makingconnection with the line for operating said relay, substantially asdescribed.

7. The combination with a telephone-line and a plurality of individualconnection-tcrminals for the line situated at the several sections of amultiple switchboard and normally disconnected from said line, of asignal for said line, a relay distinct from said signal, and meansactuated by the act of making connection with the line at any one ofsaid connection-terminals for operating said relay to connect saidconnection-terminals with the line, substantially as described.

8. The combination with a telephone-line and an individualconnection-terminal for the line normally disconnected therefrom, of asignal for said line, a local circuit, a relay distinct from said signaland a source of current therein, and means actuated by the act of makingconnection with the line for closing said local circuit to actuate saidrelay and thereby connect said terminal with the line,

substantially as described.

9. The combination with a telephone-line and a connection-terminal inthe form of a spring-jack or switch-socket, of a connectingplng, meansactuated by the insertion of said plug in the socket for connecting saidterminal with the line, and means actuated by the spring-jack orswitch-socket, of a connectingplug, a relay for controlling the circuitto said connection-terminal, a local circuit including said relay,normally-separated contacts at the switch-socket, and means for closingsaid contacts by the insertion of the connecting-plug in said switch-socket, substantially as described.

11. The combination with a telephone-line and an individualconnection-terminal for the line, of a signaling device, and means forantomatically connecting the terminal with the line and disconnectingthe signaling device therefrom, and vice versa, substantially asdescribed.

12. The combination with a telephone-line, of an individualconnection-terminal for the line and a signaling device, and means forautomatically connecting one of said elements with the line andsimultaneously disconnecting the other therefrom, substantially asdescribed.

13. The combination with a telephone-line, of an individualconnection-terminal for the line normally disconnected therefrom, asignaling device normally connected therewith, and means actuated by theact of making connection with the line for connecting said terminal withthe line and for disconnecting said signal device therefrom,substantially as described.

14. The combination with a telephone-line, of a connection-terminal, asignaling device, and means actuated by the act of making connectionwith, the line for connecting said terminal therewith and fordisconnecting said signaling device therefrom, and means actuated by theact of un making connection with the line for disconnecting saidterminal therefrom, and for connecting said signaling device therewith,substantially as described.

15. The combination with a telephone-line, of a connection-terminal anda signaling de vice, and means for automatically connecting saidelements with, and disconnecting the same from, the line so that both ofsaid elements are never in connection with the line at the same time,substantially as described.

16. The combination with a telephone-line, ofa con nection-terminalnormallydisconnected therefrom, a signaling device normally connectedtherewith, a relay,and means actuated by the act of making connectionwith the line for operating said relay to connect said terminal with theline and to disconnect said signaling device from the line,substantially as described.

17. The combination with a telephone-line, of an individualconnection-terminal for the line, a relay for connecting the same withand disconnecting the same from the line, and a test-circuit controlledby said relay, substantially as described.

18. The combination with a telephone-line, of an individualconnectionterminal for the line normallydisconnected therefrom,a relay,and means actuated by the act of making connection with the line foroperating said relay to connect said terminal with the line, and atest-circuit controlled by said relay, substantially as described.

19. The combination with a telephone-line,

' of a relay havinga Winding included in a local circuit includingcontacts at a connectionterminal, a pair of springs or other movableparts actuated by said relay, and connected respectively with the limbsof said telephoneline, back contacts against which said springs or partsnormally rest and a signaling device connected between said backcontacts, front contacts with which said springs or parts engage whenthe relay is energized, and the line-contacts of a connection-terminalconnected with said front contacts, substantially as described.

20. In a divided-multiple telephone system,

a metallic circuit-line, a plurality of linesignals normally connectedwith said line, one at each division of said system, a plurality ofspring-jacks normally disconnected from said line, a connecting-plug, arelay adapted when said plug is inserted in any of said jacks todisconnect said signaling devices from said line and to connect saidspring-jacks with said line, and means connected with said line forselectively displaying any one of said signals when said line is in itsnormal condition, substantially as described.

21. In a telephone system, a line having two limbs extending to acentral office, a relay having a movable contact member for each limb ofsaid line, a signal included in circuit between the back contacts ofsaid members, a spring-jack normally disconnected from said line andhaving its talking contacts included between the front contacts of saidrelay members,and a local circuit including the coil of said relaycontrolled at the spring-jack, whereby said signal is disconnected fromsaid line and said jack is connected with said line when a connection ismade at the jack, substantially as described.

22. In a telephone system, a line having two limbs extending to acentral office, a relay having a movable contact member for each limb ofsaid line, a signal included in circuit between the back contacts ofsaid members, a spring-jack normally disconnected from said line andhaving its talking contacts included between the front contacts of saidrelay members, and a local circuit controlled by additional contacts atthe springjack, whereby said signal is disconnected from said line andsaid jack is connected with said line when a connection is made at thejack, substantially as described.

23. In a telephone system, a line having two limbs extending to acentral oftice, a relay having movable contact members in which saidlimbs terminate, a signal included in circuit between the back contactsof said members, a plurality of spring-jacks normally disconnected fromthe line arranged at the several sections of a switchboard, said jackshaving their respective talking contacts connected together and to thefront contacts respectively of said relay members, and a local circuitincluding the coil of said relay having branch connectionsterminating inadditional contacts at each jack, whereby said signal is disconnectedfrom said line and said jacks are connected with said line when aconnection is made at any of said jacks, substantially as described.

In witness whereof I have hereunto subscribed my name in the presence oftwo witnesses.

FRANCIS W. DUNBAR.

Witnesses:

Knnrsrnn B. MILLER, CHAS. O. BULKLEY.

